In LTE-A, wider bandwidth, up to 100M will be used to satisfy the higher data rate requirement. For backward compatibility, this 100M bandwidth will be separated into multiple carrier components. Each carrier component has the maximum bandwidth of 20M. Therefore, five carrier components can be used for the user equipments in LTE-A.
Now 3rd Generation Partnership Project has agreed with the application of the downlink carrier component activation/deactivation concept basically. That is, when a base station decides not to use an activated carrier component, it de-activates the downlink carrier component and informs a user equipment to enable the user equipment not to monitor PDCCH on this carrier component so as to achieve the power saving purpose.
Additionally, according to the agreement achieved by 3GPP, the downlink carrier component de-activation/activation command is sent to a user equipment by a MAC CE signaling from a base station.
For the carrier aggregation technology, another important agreement achieved by 3GPP is that for any one of the downlink carrier component/the uplink carrier component, there is a downlink carrier component associated therewith, to be responsible for sending the downlink assignment/uplink grant information of the downlink carrier component/the uplink carrier component. And those associated information is sent to a user equipment through a radio resource control signaling (RRC signaling) from a base station.
From the perspective of a user equipment, there are two events which results that a downlink carrier component is not useable. Event 1: a RRC signaling is received from a base station to indicate that a downlink carrier component is de-configured; Event 2: a MAC CE signaling is received form a base station to indicate that a downlink carrier component is de-activated.
The difference of these two events is that, event 1 means a user equipment will be no longer perform downlink measurement on the de-configured carrier component; and event 2 means a user equipment will still continue to perform mobility relevant measurement on the de-activated downlink carrier component. But the similarity for these two events is that the user equipment will be no longer to monitor PDCCH channel on this downlink carrier component and to execute PDSCH operation, which will result in the occurrence of the following problems:
1) For the downlink carrier component, the user plan operation at the user equipment side will be affected, because the reception related to this downlink carrier component is stopped;
2) If the downlink carrier component is associated with other at least one downlink carrier component/uplink carrier component, for example, the downlink carrier component is responsible for sending downlink assignment/uplink grant information of the at least one associated downlink carrier component and uplink carrier component, then, since the user equipment can no longer receive those downlink assignment/uplink grant information associated with the downlink carrier component and the uplink component, the use of those associated downlink carrier components/uplink carrier components will be affected.
In the prior art, a scheme for reducing the impact on a user plan operation when a downlink carrier component is de-activated is provided. Its main point is that a user equipment delays the de-activation implementation until all pending HARQ transmissions and retransmissions on the de-activated downlink carrier component end when it receives the de-activation command from a base station, so as to avoid data loss and reduce the impact of the HARQ re-ordering procedure. But there are following disadvantages in the scheme, that is, de-synchronization on the de-activated downlink carrier component status between a user equipment and a base station may occur, and the base station has to schedule further transmission on the de-activated carrier component.